25
Book Reviews
Cannabis Medicines
Six books on Cannabis, published in the US and Canada in 1998 and 1999, will be reviewed. The Institute of Medicine Report, issued in March 1999, has gathered the most world-wide attention (Joy et al. 1999). A chapter of the second book, a comparison of the health effects of Cannabis with alcohol, nicotine and opiates, led to a controversial discussion in spring 1998 and is now published along with 14 other papers on the health effects of Cannabis (Kalant et al. 1999). The third and largest book covers a conference on "Marihuana and Medicine" in May 1998 in New York, edited by scientists that oppose the medical use of Cannabis (Nahas et al. 1999). The fourth is a practical guide for patients, written by three physicians who are promoting legal access to medical marijuana (Zimmermann et al. 1998). The fifth, written by a journalist, describes the US Governments handling of the marijuana issue and accuses them of dishonesty by focusing mostly on recreational use (Ford 1998). The sixth has been written by a marijuana patient who is describing the political and scientific discussion in the US over the last 25 years from a personal point of view (Randall and O’Leary 1998).
Joy, J. E., Watson, S. J., Benson, J.A (eds): Marijuana
and Medicine: Assessing the Science Base.
Institute of Medicine, National Academy Press, Washington DC,
1999, 290 pages
On 17 March 1999, Stanley Watson, Co-director and research
scientist, Mental Health Research Institute, University of Michigan, and John
Benson, Dean and Professor of medicine emeritus, Oregon Health Sciences
University, presented the second Institute of Medicine Report (IOM) on
marijuana, the first being published in 1982. It was ordered by the White House
Office of National Drug Control Policy in January 1997 as a reaction to
successful ballot state initiatives in California and Arizona in November 1996,
allowing the medical use of marijuana for seriously ill patients. The thorough
and factual reports say that marijuana is potentially effective for some
symptoms and recommends rigorous clinical trials and the development of a
delivery system that eliminates the harmful effects of smoking. Beyond the harms
of smoking, the range of problems associated with medical marijuana were within
the acceptable range of problems associated with other medications. Further, it
states that marijuana could be allowed for medical use, without increasing
non-medical use. The authors say there is "no convincing data to support
this concern," and they note that "this question is beyond the issues
normally considered for medical uses of drugs." It makes six
recommendations, including clinical trials allowing patients with chronic
conditions or end-stage diseases, who have no other alternative, to use
marijuana on an experimental basis for six months.
The assertation of the IOM report that single cannabinoids
are more suitable for reproducing the desired therapeutic effects than the whole
plant is irritating for a reader from a country where the use of herbal products
is widespread in medicine. It has not much to do with reality. Neither THC nor
Nabilone act more selectively than a standardised extract of the Cannabis
plant. The idea of pure agents for a specific effect is a dream of medical
science never realised until now. Drug therapy always has to do with
interindividual and intraindividual variability of a lot of parameters: age,
gender, general health status, concomitant disease, interaction with other
drugs, resorption, function of spleen and liver etc. There is no hint that the
variability of the components of Cannabis with the exception of THC and
CBD plays a major role in the reproducibility of effects in comparison to these
and other parameters.
However, the new IOM-Report is a valuable review on the
matter and understandable by non-scientists. It presents the political
background, examples of successful medical uses of the drug, the pharmacology
and animal physiology, the consequences and side-effects of marijuana use, the
medical value of marijuana and related substances and the development of
cannabinoid drugs.
Kalant, H., Corrigal, W. A., Hall, W., Smart, R. G.: The
health effects of Cannabis.
Centre for Addiction and Mental Health, Toronto, Canada,
1999, 540 pages.
One of the 15 chapters of the book raised much interest and
controversy about one year before it was published. It was only available as a
manuscript then, as one of the background papers for the Cannabis report
of the World Health Organization of December 1997 ("Cannabis: a
health perspective and research agenda"). According to the New Scientist of
February 1998, officials of the WHO in Geneva had suppressed the paper, because
when comparing the health effects and psychological risks of alcohol, Cannabis,
nicotine, and opiate use, it had shown the lowest risk for Cannabis. The
WHO claimed in reply to the reproach of censorship, that this part was not
included in the WHO review due to scientific reasons. Another chapter evoked
some media resonance in the beginning of this year when the entire collection of
papers was published as a book, edited by Wayne Hall, head of the Australian
National Drug and Alcohol Research Centre, and scientists of the Canadian
Addiction Research Foundation. It was the chapter on "Marijuana: on-road
and driving simulator studies" by Alison Smiley. She had told the press
that people who smoke moderate amounts of marijuana were not much more dangerous
behind the wheel than completely sober drivers, because people under the
influence of Cannabis would compensate for their impaired performance by
driving more slowly and cautiously.
People who want to get an overview of the chemistry,
pharmacology and possible adverse effects of Cannabis will find in these
articles well-balanced information on the relevant discussion lines and a good
review of the most important primary literature. Articles deal with the
influences of Cannabis on different body systems and functions, the
central nervous system, behaviour, cell nuclei, immunity, respiratory system,
reproductive function, pregnancy, the cardiovascular and the gastrointestinal
system. Conclusions are usually not final but rather an intermediate description
which tries not to fall into the trap of "problem inflation" and
"problem deflation", in cases where our knowledge is still limited.
The book is a valuable reference and review, as are earlier reviews initiated by
governmental institutions or international organisations, the two Institute of
Medicine reports (1982, 1999), the Australian report by Hall, Solowij and Lemon
(1994) and the WHO report of 1981 (Fehr and Kalant, 1983).
People who want to get an overview of the medical use of Cannabis
will be disappointed. If science aims to get an image of the world, this chapter
documents that science has failed to a great extent in assessing the therapeutic
potential of Cannabis and the cannabinoids. And it demonstrates what
happens when experience on a therapeutic topic is drawn only from printed paper
and not from contact with patients. What is presented by Christine R. Hartel is
a very limited and reserved look at the issue. This leads to the strange
situation that there are patients with multiple sclerosis, Tourette’s
syndrome, epilepsy, glaucoma, and other illnesses that have strong relief from Cannabis,
confirmed by many physicians and that on the other hand you will read in this
chapter "that THC and marijuana are not considered candidates for drug
development for this indication," or that "further controlled research
is indicated before conclusions can be drawn". The reader will miss some
interesting studies in this 10 page review, the study by Brenneisen and
colleagues (1996) on spasticity, the study by Holdcroft et al. (1997) on
pain and the study by Volicer (1997) on Alzheimer’s disease.
Hartel takes adverse effects due to the illegal status of Cannabis
as arguments against legal medical access: Smoking causes harm, plant material
may be contaminated, potency may be variable. These problems would not exist if
there were a legal supply of standardised Cannabis which could be inhaled
by the use of vaporisers that are already available. In sum, the book provides a
limited picture of the medical use of Cannabis.
But it provides a valuable overview on its pharmacology and
toxicology. It is much recommended for people who want to get a more than
superficial overview and a deeper insight into the research of the last three
decades and the actual discussion.
Nahas, G., Sutin, K. M., Harvey, D. J., Agurell, S.: Marihuana
and Medicine.
Humana Press, Totowa, NY, 1999, 848 pages.
This is a collection of papers mostly concerned with
"the pharmacological and molecular basis of the therapeutic properties of
marihuana and its active ingredient, THC" as explained in the books
introduction. The popular topic "therapeutic properties of marihuana"
seems to be used (or misused) to present, above all, the real, presumed or
pretended dangers connected with the recreational use of Cannabis. The
book follows the conference of the International Cannabinoid Research Society on
"Marihuana and Medicine" in May 1998 at New York University School of
Medicine, headed by Gabriel Nahas, a well-known opponent of the medical use of
marijuana.
Relevant and not so relevant information, reviews and
original articles are mixed up in a book covering 850 pages. We find a text on
"Suppression and induction of aggressive reactions by chronic and acute (delta-9-tetrahydrocannabinol)
treatment in laboratory rats" or on the "Detection of Cannabis
in victims of violent death in Stockholm" which looks rather strange in a
book that claims to present the basis for the therapeutic use of the drug. To
cite the IOM report these topics are "beyond the issues normally considered
for medical uses of drugs."
These and many other chapters give the whole book a rather
sceptical look concerning the topic without analysing their relevance for the
therapeutic situation in humans. The unprepared reader will sometimes be more
led astray than well-informed. But there are many other relevant and
well-presented articles, e.g. on the mechanisms of analgesia, control of
nausea and vomiting and other effects, which are interesting for those who want
to get a deeper insight into the issue and are able to separate the relevant
from irrelevant information.
Zimmermann, B., Bayer, R., Crumpacker, N.: Is marijuana
the right medicine for you.
Keats Publishing, New Canaan, Conneticut, 1998, 208 pages.
The book focuses on the practice of the medical use of
natural Cannabis and THC, intending to give people a step-by-step
introduction to the topic, giving answers to questions that might arise. Twelve
of the 20 chapters deal with indications (AIDS, glaucoma, nausea, multiple
sclerosis etc.), the others with possible adverse effects, practical hints for
getting and using marijuana and the political discussion. It is perceivable that
it is written by physicians that have practical experience in the assistance of
patients, among them Bill Zimmermann, director of Americans for Medical Rights
which fights for access to medical marijuana. The authors take the experience of
patients seriously and are ready to learn from them, citing the motto of a
medical school: "The patient is the text book". It is really "a
factual guide to medical uses of marijuana". The authors neither exaggerate
the medical value of the plant in terms of "wonder" or
"miracle", that often leads to disappointment in patients if marijuana
should not work, nor do they undervalue the medical quality solely because a
certain effect, that is well known by hundreds of patients and physicians, has
not been proven in a randomised double-blind trial.
Concerning some possible long-term effects the book is
sometimes too definite, regarding the ongoing discussion in this area. This may
be in part due to limited space and to the wish to not bother the reader with a
complex discussion. There are some points that might be considered in the next
edition, e.g. in the part on sterilising marijuana it is said that 190(C
(374(F) should not be exceeded in this process, but it was found in a study by
Brenneisen and colleagues, that a temperature of 200oC for five to ten minutes
seems to be the optimum temperature for the decarboxylation of THC-acid. So
there is no need for a strong warning.
I do recommend this book very much. It is one of the best of
those written to help patients get an introduction and overview of the medical
usefulness of Cannabis products and how to use them.
Ford, D. R.: Marijuana: not guilty as charged.
Good Press, Sonoma, California, 1998, 253 pages.
This book is a plea for the legalisation of marijuana for
medical and recreational use. The author describes the hypocrisy, stupidity and
cruelty of marijuana policy in the United States through a series of unrevealing
stories and well known and less well known documents. They demonstrate the
ignorance of arguments and the harmful consequences of marijuana prohibition.
The reader develops a feeling of rage and powerlessness on a culture of the
Middle Ages where revenge rules and rationality still has no place.
There is a strong tendency in the book to mix the medical and
the recreational use and to use or misuse patients with severe illnesses as an
example of the cruelty of the war on drugs. ("The ill and the dying are the
primary losers when it comes to marijuana prohibition."). It is a book that
tries to move emotions, not shrinking from using the strongest phrases and the
most dramatic comparisons ("the slaughter of marijuana"). Possible
side effects are generally minimised ("Marijuana is not any more physically
addictive than ice-cream"). I am always irritated about this way to
aggravate or minimise and it makes me sceptical about the honesty of the author.
Mutual irrationality seems to be typical for both sides in the war on drugs.
Could it be that the inflationary use of extreme comparisons and allegories and
the low practice of differentiating on both sides of the discussion is a cause
for some complications in the struggle for the reintroduction of Cannabis
as a medicine and Cannabis as a crop? This book leaves you with a very
mixed impression.
Randall, R. C., O’Leary, A. M.: Marijuana RCS: the
patients’ fight for medicinal pot.
Thunder’s Mouth Press, New York, 1998, 498 pages.
The book by Robert Randall, the first American to get legal
access to medical marijuana in 1976, and his partner Alice O’Leary tells the
story about 25 years of struggle for legal access to the therapeutic use of Cannabis
in the US. In 40 chapters the beginnings of the movement, the first changes of
state laws, the introduction of Marinol®, the foundation of organisations
advocating the medical use of marijuana and the hopes and tragedies are
presented in a narrative and tightening way.
The open manner that does not stop short of criticising
exponents of the marijuana movements gives the reader a deep insight into
different aspects of the developments in the last decades. He is not only
attacking the governmental institutions and judges that deny patients marijuana
for therapeutic purposes but also exponents and organisations of the marijuana
movement, that in the eyes of Randall misuse the medical issue for drug policy
("Drug ideologues to the left and right."). Most of the book is
biographical with a lot of lively dialogues that describe the experiences of ups
and downs within the long struggle of the co-founders of the Alliance for Cannabis
Therapeutics.
Worth mentioning is the foreword of Lyn Nofziger, former
White House director of communication and chief speech writer for Ronald Reagan.
Telling a story from his family he promotes the medical use of marijuana.
"Strange as it may seem, here is one right-wing Republican who supports
carefully controlled, medical access to marijuana. (...) A doctor should have
every possible medication — including marijuana — in his armentarium."
I enjoyed reading the book. I do not know if it tells the
"truth about the patients’ fight for medical pot", as is claimed in
the advertisement, but at least it tells of one which is worth reading and
knowing about.
Franjo Grotenhermen
nova Institute
Huerth in the Rhineland, Germany
Alkaline Hemp Woody Core Pulping -
Impregnation characteristics, kinetic modelling and
papermaking qualities
Dissertation by Birgitte de Groot: A thesis success-fully
defended by the respondent at the oral dissertation on Oct. 10th 1998 in partial
fulfillment for the doctor degree in Chemical Engineering at the University of
Agriculture in Wageningen, The Netherlands.
An intense search, during the 1980s, for a complementary
non-food crop had shown that fibre hemp (Cannabis sativa) could be grown
on Dutch farmland with considerable agricultural advantages. However, when
Birgitte de Groot began her research within the framework given by The Dutch
Hemp Programme about 10 years ago, the crucial question was, whether or not a
hemp harvest could be used in any large-scale, industrial (non-food)
application.
The dissertation consists of the following chapters:
General Introduction.
Alkaline swelling of hemp woody core. (Published 1997 in J. Wood Chem. Technol. 17(1,2): 187-208)
Simplified kinetic modelling of alkaline delignification of hemp woody core. (Published 1994 in Holzforchung 48(3): 207-214)
Alkaline pulping of hemp woody core: kinetic modelling of lignin, xylan and cellulose extraction and degradation. (Published 1995 in Holzforchung 49(4): 332-342)
Alkaline woody core pulping: pulp and paper characteristics. (Accepted for publication in The Tappi Journal)
General discussion.
The major part of the dissertation presents the results from her exploratory work in the laboratory, and is thus focused upon the possibility of using hemp woody core soda pulp for paper. The woody core, the inner 2/3 of the stalk, has usually been discarded or disposed of as a fuel, while the outer part (the bast) has been an important filament in the rope and yarn manufacturing industries for centuries. Chapters 2-5 report the results obtained. Each chapter (except nos 1 and 6) is written in the form of an article manuscript ready to publish, the majority of which had already been accepted by the time of the dissertation publication. The dissertation ends with a chapter, in which some quality aspects of hemp woody core soda pulp as a source of papermaking fibres are explored.
Chapter 1: General Introduction. The dissertation starts
with a review that covers subjects as diverse as plant anatomy, fibre morphology
and fibre cell wall ultrastructure. It then introduces chemistry, the physics of
porous solids, the fundamentals of polymer degradation, the concept of
heterogenous reactions (particularly those between reactants in a liquid phase
and reactants in a visco-elastic porous solid phase), the transport of
degradation fragments out of the cell wall etc. In other words, the nature of
swelling and the impact of changing porosity of plant tissue during impregnation
and pulping.
The striking similarities between the overall morphology and
chemistry of hemp woody core and many hardwoods presently being used in the pulp
and paper industry makes it to seem obvious that the use of non-woods in general
and hemp woody core in particular (1) as a potential source of papermaking
fibres, needs further investigation.
Chapter 2: Alkaline swelling of hemp woody core. Reported
is on an interesting study of the first stage of the pulping operation, the
impregnation stage, during which the fibre cell walls swell and are filled with
pulping liquor.
By employing a multitude of rather sophisticated physico-chemical
techniques, the author(s) conclude;
• that the extent to which alkali swells the woody core
tissue correlates well with the xylan:lignin ratio of that tissue [actually in
support of the "spring (hydrophilic hemicellulose, expanding/swelling) and
bar (hydrophobic lignin, rigid/ restricting) model", suggested by Stone and
Scallan (2);
• that this is the very first time evidence for the
existance of 2-3 separate pore systems within the swollen fibre has been
obtained [actually in support of the postulated existance of what was called
"microreticular" and "macroreticular" pore systems within
the cell wall, suggested by Stone and Scallan (3)];
• that the material/hemicellulose/xylan removal and the
increased pore sizes/pore volume in the swollen cell wall influences the
subsequent course of component degradation/delignification and might therefore
be necessary for fibre separation and fibrillation [actually in support of the
idéas explicitly brought forward by Goring et al. (4)].
Chapter 3: Simplified kinetic modelling of alkaline
delignification of hemp woody core and Chapter 4: Alkaline pulping of
hemp woody core: kinetic modelling of lignin, xylan and cellulose extraction and
degradation. These constitute the central portion of the study and will
therefore be treated together.
Soda (aqueous NaOH) pulping (a common method of non-wood
delignification) in a continuous flow reactor and quantitative analytical
assessments of the component removal of hemp woody core at various stages of
delignification resulted in sets of data that were fitted with good precision to
exponential expressions. These expressions describe chemical reaction kinetics, i.e.
the influence of temperature and duration on the extent and the rate of chemical
reactions.
The delignification of woody core by the soda method at
reaction conditions similar to those prevailing in a laboratory continuous flow
reactor (constant temperature, constant soda concentration and constant flow)
demonstrated that
• the removal of xylan (hemicellulose) facilitated the
subsequent removal of lignin (see above);
• the best fit to the experimental data was obtained if the
three subsequent delignification modes (initial, bulk and rest/residual) that
usually describe wood pulping were reduced to two and these were assumed to take
place simultaneously rather than consecutively.
In passing, a very important remark was made, that it is
evident that the parameters in the kinetic expressions must be looked upon as
being the mathematical expression of lumped overall reaction parameters.
It is interesting to compare these results with those
obtained for the kraft and soda delignification kinetics of wheat-straw in a
batch reactor, as described by Lindgren et al. (5). Although the
course of pulping in the latter study was fitted to a three stage
delignification model, it was found that the wheat-straw lignin was removed to
about 90% initially, and that only 1-2% was removed in the bulk stage. The
similarities between the modes of delignification of these non-woods are
striking. In comparison, only 15-20% of wood lignins are removed initially.
The second central paper (Chapter 4) expands the kinetic
expressions to describe the removal of lignin, xylan and cellulose during the
course of soda pulping in a continuous flow reactor.
The classic experimental techniques to study chemical
reaction kinetics, either in a batch or a continuous flow set-up, are far from
full-scale mill reality, as they are made under controlled and idealized
conditions. They also have shortcommings as a means of getting detailed
information about the multitude of complex, simultaneous physico-chemical
reactions that are taking place. Not withstanding this, however, knowledge about
the relative importance and influence of "lumped parameters of overall
reaction patterns" is better than nothing. Ultimately it may lead to
improved processes (6).
Chapter 5 (Alkaline woody core pulping: pulp and paper
characteristics).This is the final chapter of the dissertation
containing experimental data and deals with the evaluation of the paper
properties of hemp woody-core soda pulps.
Again, by a ambitious comparison of data from
(semi-empirical) physical testing of (apparent) bulk, e.g., tear
resistance, tensile strength, burst strength, drainage resistance, brightness
and opacity at different degrees of beating, with those obtained for some
fundamental physico-chemical properties of the corresponding samples, such as
the detailed chemical composition, and the molecular chain-length/polymerization
degree [DP] and crystallinity of the cellulose, some very interesting and rarely
seen relationships are examined.
Based on the results obtained, the following observations and
conclusions about hemp woody core pulp for paper may be drawn, although this was
not always done in the dissertation. Qualitative comparison with hardwood pulp
(Birch, Betula sp.) and agreement (=) and disagreement (±) with other
non-woods has been made by the reviewer (7). Hemp soda pulp:
• develops very high drainage resistance when beaten (=)
• (apparent) bulk decreases on beating (=)
• burst is linearly correlated with tensile (=)
• tensile is adequate (=)
• tear is (very) low (±,=)
It was further demonstrated that for hemp soda pulp:
• the impact on paper strength (tear) appeared to be
negligable when DP is higher than 1000. [In other words the "rule of
thumb" regarding paper strength was nicely confirmed];
• the constant added to the rate equation for the
degradation of cellulose (in terms of decreasing DP) found in the dissertation,
suggested that a certain fraction of the cellulose, with ² 512 glucose units
per cellulose polymer molecule, was more resistant to soda pulping than the rest
of the cellulose [in close agreement with the "Fringed Micellar Model (8)].
The most serious shortcomings of the dissertation are
concentrated in Chapter 5, in which the important question concerning the value
of hemp woody core soda pulp for paper is dealt.
In spite of the multitude of measurements and data that are
presented (although nowhere in the dissertation is listed a full set of original
data for Chapter 5) many quite obvious and interesting lines of thoughts seems
to be dropped "half way". For example, the DP/crystallinity effect on
fibre and paper strength is not completed.
Some further critical remarks can be made concerning the
presentation of ‘s’ (the specific light scattering coefficient in the
Kubelka-Munk theory) as applied to the interaction between light and a
particulate sheet of pulp or paper, seems a bit confusing. The confusion arises
from the basic question: is ‘s’ being caused by ALL the unbonded, free fibre
surfaces in the sheet or is the opacity of a sheet (at equal brightness, or
rather, constant ‘k’) dominated by the contribution to light
reflection/scattering of the outer boundary surfaces of the sheet? An
elucidating discussion concerning this and related questions can be found in the
literature (9).
Also in this dissertation:
• the hemp woody core soda pulps were actually not compared
(in terms of parallell experiments) with some "well accepted"
hardwood, non-wood and/or recycled pulps;
• the relevant long fibre - short fibre (hemp woody core
soda pulps) mixtures for printing and writing papers were not studied.
Without such or similar experiments, the
"question/s" put forward in the introduction (whether or not hemp
woody core soda pulp is suitable for printing and writing paper) can only be
given an incomplete and indicative answer, viz:
• "yes", incontrovertibly, the fibre hemp woody
core can successfully be pulped by the soda method,
• "maybe" the pulp is good enough as a short
fibre component substituting for other easily available short fibre pulps
(hardwood or non-wood) for printing and writing grades of paper.
Hence, the above second crucial issue needs further
investigation, which the "respondent" correctly points out in her
dissertation: "Therefore it is conceivable to further develop alkaline
woody core pulping for purposes as hardwood and straw pulp, as a component in
pulp mixes for printing grade paper."
Chapter 6: General discussion.
The dissertation ends with a general discussion of the
fundamental knowledge and state of the art of "alkaline hemp woody core
pulping - impregnation characteristics, kinetic modelling and papermaking
qualities", now including the results of the dissertation.
Whether or not the results of the dissertation will ever come
to practical use only future can tell. However, it contains some very
interesting relationships and data, that immediately strengthen and widen our
knowledge!
Per Ahlgren
Prof. Fibre properties
Pulp & Paper Technology
University of Karlstad
Sweden
E-mail: per.ahlgren@kau.se
(1) | In passing, the reader is reminded of the important fact, that the complication often encountered in alkaline non-wood pulping, i.e. the need for desilication, is only actual when pulping monocot grass species) and not when pulping dicots (eg. hemp), as they are naturally low in silicon compounds. |
(2) |
Stone, J.E. and Scallan, A.M. (1967) Tappi 40, 496. |
(3) | Stone, J.E. and Scallan, A.M. (1968) Pulp Paper Mag.Can. 69, T288. |
(4) | Wood, J.R.; Ahlgren, P.A. and Goring, D.A.I. (1972) Svensk Papperstidning. 75, 1:15. |
(5) | Gonzalo Epelde, I., Lindgren, C.T. and Lindström, M.E. (1997) "Kinetics of wheat straw delignification in soda and kraft pulping" in C.T. Lindgren’s Doctoral Thesis, Royal Institute of Technology, Stockholm, Sweden, Sept. 23. |
(6) | Kraft pulp is today manufactured with higher yield, higher viscosity and lesser remaining (residual) lignin (that eventually has to be removed by bleaching), with no loss in fibre or paper strength than previously was possible, due to studies of delignification kinetics like the one presented in the "Hemp thesis". Recent examples are "Modified Kraft Cooking" and "Isothermal Kraft Cooking", the predominant varieties of softwood kraft pulping employed in the kraft mills today. See for example; Hartler, N. (1978) Svensk Papperstidning. 81, 15: 483; Nordén, S. and Teder, A.(1979) Tappi Journal. 62, 7: 49; Dillner, B. (1993) Svensk Papperstidning. 96, 2:22; Sjöblom, K. (1997) "Improved Selectivity in Kraft Cooking through Changes in the Cooking Liquor Concentration Profiles". Doctoral dissertation. Royal Inst. Techn., Stockholm; Lindström, M. (1997) "Some Factors Affecting the Amount of Residual Phase Lignin During Kraft Pulping". Doctoral dissertation. Royal Inst. Techn., Stockholm. |
(7) | Thykesson, M., Sjöberg, L-A. and Ahlgren, Per (1998) Ind. Crops & Prods, 7,351-362, complemented with hitherto unpublished results for bleached pulps. |
(8) | Fengel, D. and Wegener, G. (1989): "Wood - chemistry, ultrastructrure, reactions". Walter de Gruyter & Co., Berlin. p. 83. Frey-Wyssling, A. (1958): Science 80, 119. |
(9) | Leskelä, M and Luner, P. (1993) Paperi ja Puu 75, 8: 601-605. |